Thermal Conductive Network Regulation Of BN In Single Matrix And Immiscible Blends

With the miniaturization and high power density of electronic devices,there showed a greater demand on thermal conductive materials.In order to comply with the development of the electronic industry,researches on thermal conductive insulating composites became the necessary and key process to solve heat dissipation problems.Boron nitride(BN)has many advantages such as prominent thermal conductivity and excellent electrical insulation.These unique properties make BN an ideal filler to incorporate with polymer matrix and obtain the high thermal conductive insulating composites.However,high loading of rigid particles will badly decrease the processing properties and toughness of composites.The study of preparing BN-filled composites seems rather important.In this research,the hexagonal boron nitride(h-BN)was used as the thermal conductive filler to incorporate with polyamide-6(PA6)matrix,which offered good crystallization properties and processing ability.A series of h-BN/PA6 thermal conductive composites were fabricated by three different methods,including meltingmixing(MM),solution mixing(SM),and powder mixing(PM).The effect of h-BN amount and preparation methods on thermal conductivity,morphology,melting and crystallization behavior,thermal stability,and rheological properties were investigated.The results indicated that the thermal conductivity of PA6 composites were increasing with the increment of filler content for any one of preparation method.There showed an obviously increment on thermal conductivity of SM while the filler loading reached a certain value(25 wt%),which is called the "thermal percolation threshold".The thermal conductivity of PA6 composites prepared by solution mixing was up to 1.45 W·m-1·K-1 on 40 wt%h-BN loading,that is a 4.0-fold higher than the neat PA6.While at the same filler amount,the thermal conductivity of composites prepared by melting mixing and powder mixing were 1.13W·m-1·K-1 and 1.32W·m-1·K-1,respectively.And the experimental data were consistent with those predicted by the Agari model.It was observed from SEM images that the h-BN exhibited relatively well dispersion in PA6 phase and showed good interfacial compatibility.The addition of h-BN thermal conductive filler could result in the decrease of crystallinity,but the Xc values were always superior to those of MM and PM counterparts at the same filler content.In brief,the preparation method of solution mixing can obtain high thermal conductive thermal insulating composites.Secondly,tenary blend composites were also prepared by adding h-BN into polypropylene(PP)/Ethylene-Propylene-Diene-Monomer(EPDM)blends as the matrix via different processing methods.The micromorphology of PP/EPDM blends with different mass ratio was investigated,in order to achieve the co-continous phase structure.On the basis of this,incorporating h-BN filler into immiscible polymer blends of PP/EPDM,the selective localization states of h-BN were investigated from thermodynamics and dynamics.In addition,the influences of the selective localization of h-BN on the thermal conductivity and melting and crystallization behavior of h-BN/PP/EPDM composites were also investigated.It was found that the mixing strategy could directly influence the localization of thermal conductive filler in co-continuous blends.For the h-BN/PP/EPDM composites based on mixing sequences,when the h-BN was first dispersed in PP phase(h-BN/PP master batch),they remain well dispersed in PP.When the h-BN was first dispersed in the EPDM copolymer or when the three components were simultaneously mixed,part of h-BN will migrate to the interface although some of them stay in the EPDM phase.For the h-BN/PP/EPDM composites based on mixing time,with the increase of mixing time,h-BN particles keep migrating from one phase(EPDM)to another(PP).Which indicated that the h-BN has a tendency to preferentially localize in the PP phase during the mixing process and it was consistent with the thermodynamic prediction.The thermal conductivity test confirmed that in all blends,the h-BN exclusively located in PP phase can obtain a higher thermal conductivity,which was up to 0.81 W·m-1·K-1 at the h-BN loading of 10wt%,revealed a 2.6-fold gain compared to PP/EPDM polymer blends.And the thermal conductivity of tenary composites with 40 wt%h-BN reached 1.37W·m-1·K-1 which obtained a 47%increment in comparison to that of h-BN/PP composites,at the same filler loading.The influence of h-BN and EPDM on the crystallization behavior of PP polymer were also studied.It was found that the addition of h-BN and EPDM will obviously decrease the crystallinity(Xc)of PP.